Mono- and di-(lower alkyl substituted) dicyclopentadienyl iron



United States Patent 3,285,946 MONO- AND DI-(LOWER ALKYL SUBSTITUTED)DICYCLOPENTADIENYL IRON Earl G. De Witt, Royal Oak, and Jerome E. Brownand Hymin Shapiro, Detroit, Mich, assignors to Ethyl Corporation, NewYork, N.Y., a corporation of Virginia No Drawing. Filed Nov. 23, 1955,Ser. No. 548,755

2 Claims. (Cl. 260-439) This application is a continuation-in-part ofour prior co-pending applications Serial No. 417,919, filed March 22,1954, and now abandoned, and Serial No. 297,392, filed July 5, 1952.

This invention relates to alkylated dicyclopentadienyl iron compoundsand their use as antiknock materials.

It is an object of this invention to provide new compositions of matter.A further object is to provide liquid hydrocarbon fuel containing thesenew compositions of matter wherein the fuels possess superior antiknockqualities. A further object is to provide new antiknock agents andantiknock fluids.

We have discovered new compositions of matter which comprise alkyldicyclopentadienyl iron wherein the cyclopentadiene radicals aresubstituted with 1 to 10 alkyl groups containing 1 to 10 carbon atoms,the total number of the carbon atoms in the alkyl groups being 1 to 32.An outstanding example of this new class of compounds isbis-(methylcyclopentadienyl) iron. We have also discovered that byblending these new compositions of matter with liquid hydrocarbon fuelsto obtain a liquid hydrocarbon fuel containing alkyl cyclopentadienyliron wherein the cyclopentadiene radicals are substituted with 1 to 10alkyl groups of 1 to 10 carbon atoms, the total number of the carbonatoms in the alkyl groups being 1 to 32, we obtain fuels of superiorantiknock characteristics. We have also discovered new antiknock fluidscomprising organolead antiknock agents, scavengers for these antiknockagents, and alkyl dicyclopentadienyl iron of the type described.

The new compounds of this invention are superior as antiknock agentsbecause they not only possess exceptional antiknock activity but theyalso combine to a high degree the ancillary properties necessary for asuccessful commercial antiknock. Thus, for example, our compounds aresuperior because of their favorable solubility, volatility, and state ofaggregation characteristics (eg melting point). Being liquids or lowmelting solids or semi-solids soluble to a high degree in liquidhydrocarbons, they are easily blended with gasoline and are readily andsmoothly inducted with the gasoline into the combustion chamber of theengine where they exert their antiknock effect. Because of their goodvolatility characteristics they are also distributed equitably among thecylinders of a multi-cylinder engine.

The compounds of this invention all contain iron as the central metallicatom, and to this iron atom are attached two cyclopentadiene rings.These rings contain 1 to 10 alkyl groups of 1 to 10 carbon atoms, thetotal number of the carbon atoms in the alkyl groups being 1 to 32. Thealkyl groups included within this invention are therefore the methyl,ethyl, n-propyl, isopropyl, nbutyl, isobutyl, sec-butyl, tert-butyl, andall the isomeric amyl, hexyl, heptyl, octyl, nonyl, and decyl groups.

In one embodiment of our invention one of the cyclopentadiene ringscontains 1 to 5 alkyl groups of 1 to carbon atoms, the total number ofthe carbon atoms in the alkyl groups being 1 to 32, and the othercyclopentadiene ring is unsubstituted. This embodiment includes themono-, di-, tri-, tetra-, and pentaalkyl cyclopentadienyl irons whereall the alkyl groups are on one cyclopentadiene ring. Using forconvenience the generic it will be seen that this embodiment includesmonomethyl ferrocene, monoethyl ferrocene, monobutyl ferrocene,monodecyl ferrocene, 1,2-dimethyl ferrocene, 1,3- dihexyl ferrocene,1,2,3-triis-opropyl ferrocene, 1,2-dimethyl-4-octyl ferrocene,1,2,3,4-tetraethyl ferrocene, l,2,3,4-tetraheptyl-5-butyl ferrocene, andthe like. Ac cording to present understanding of the ferrocene molecule,all the positions of any one cyclopentadiene ring in ferrocene areequivalent to each other with respect to the iron atom so that there isonly one monoalkyl ferrocene. In the case of the diand trialkylferrocenes, positional isomerization is possible. In our nomenclature,this is indicated by numerical prefixes to the names of the compounds.

Another embodiment of the invention comprises alkyl dicyclopentadienylirons or alkyl ferrocenes wherein the cycl-opentadienyl radicals aresubstituted with 2 to 10 alkyl groups of 1 to 10 carbon atoms, the totalnumber of the carbon atoms in the alkyl groups being 1 to 32, andwherein each of the cyclopentadienyl rings has at least one alkyl group.The nomenclature we have adopted for these compounds, except for thevery simplest ones, is to designate alkyl groups on one cyclopentadienering by unprimed numerals and to designate those on the other ring byprimed numerals (see the illustrative formula above).

In this embodiment of the invention are includedbis-(methylcyclopentadienyl) iron, bis-(ethylcyciopent adienyl) iron,bis-(decylcyclopentadienyl) iron, l,2,l-trimethyl ferrocene,1,2-dimethyl-1,2-diethyl ferrocene, 1,3-dimethyl-1',2'-didecylferrocene, 1,3,1'-trimethyl ferrocene, 1,2,3-tri-n-propyl-1-octylferrocene, 1,2-dimethyl-3-amyl-1',2-dimethyl ferrocene,1,2,3,1',3'-pentamethyl ferrocene, 1,2-diethyl-4-methyl-1-n-heptylferrocene, 1,2,4,l',2'-pentaethyl ferrocene,1,2,4-tridecyl-1,3'-dimethyl ferrocene, l,2,4-tripropyl-1,2',3'-triethylferrocene, bis-(1,2,4-trimethylcyclopentadienyl) iron,1,2,3,4,1'-pentahexyl ferrocene, 1,2dimethyl-3,4,1,2-tetraethy1ferrocene,

2,3,4,1,3 '-hexamethyl ferrocene,

,3,4,1',2,3'-heptaethyl ferrocene,v ,3,4,1,2',4'-heptamethyl ferrocene,is-(tetraethylcyclopentadienyl) iron, ,2,3,4,5,1-hexamethyl ferrocene,,2,3,4,5,l',2-heptaethyl ferrocene, 1,2,3,1-tetramethyl-4,3 'dipropylferrocene, 1,2,3,4,5-pentamethyl-1,2',3 '-trinony1 ferrocene,1,2,3,4,5-pentamethyl-1',2,4-triethy1 ferrocene, nonamethyl ferrocene,

decamethyl ferrocene,

decaethyl ferrocene,

and the like. Other compounds within this embodiment will now beapparent to those skilled in the art. For availability and for optimumqualities leading to good antiknock usage, we prefer to use thosecompounds wherein both cyclopentadienyl rings are substituted with alkylgroups, preferably of 1 to 4 carbon atoms, one on each ring, as theserepresent the most mobile liquids among our compounds. Therefore, apreferred mode of this invention comprises liquid hydrocarbon fuelscontaining .a lower alkyl dicyclopentadienyl iron in an amountsuflicient to increase the antiknock characteristics of said fuel. Weespecially prefer such compounds wherein all the alkyl groups are thesame. We have had especially good results withbis-(methyl-cyclopentadienyl) iron and bis-(ethylcyclopentadienyl) iron.

The compounds of this invention can be prepared in a variety of ways.One convenient method is the condensation of the alkali metal derivativeof the appropriate alkylated cyclopentadiene with 'an iron salt. Thealkali metal derivative of the .alkylated cyclopentadiene can in turn bemade by reaction of the alkylated cyclopentadiene with alkali metal,preferably in dispersed form or with an active 'alkali metal derivativesuch as an alkyl sodium or lithium compound.

Our compounds may also be prepared by condensation of Grignard reagentsderived from alkylated cyclopentadienes with iron salts or other ironcompounds, by Friedel-Craft alkylation of ferrocene, etc. Other meansfor preparation of our compounds will be apparent to those skilled inthe art.

Preparation of our compounds is exemplified in the following examples.

EXAMPLE I Bis-(ethylcyclopentadienyl) iron In a stirred reaction vesselprovided with a refiux condenser and liquid feed means ethyl magnesiumbromide (1 mole) is prepared in diethyl ether by the usual method. Tothe ether solution of Grignard reagent is added 1 mole of ethylcyclopentadiene, resulting in the formation of ethylcyclopentadienylmagnesium bromide. A solution of 0.5 mole of anhydrous ferric chloridein 200 parts of diethyl ether is then added to the reaction mixture overa period of approximately 30 minutes. The reaction mixture is thenmaintained at reflux temperature of about 40 C. for one hour. Themixture is then cooled and treated by adding 10 percent aqueous ammoniumchloride solution to the reaction mixture. The ether layer whichcontains the desired bis-(ethylcyclopent'adienyl) iron is separated from.the aqueous layer and the ether dried and removed by distillation. Thecrude product which is obtained as the residue from this distillation ispurified by vacuum distillation to yield pure=bis-(ethylcyclopentadienyl) iron in good yield. This productcorresponds to the formula C H Fe. This com pound boils at 130-131 C./9mm., melts at 35 C., has a refractive index 11 1.5760, and is a mobile,deep amber colored liquid with a mild camphoraceous odor.

The same technique is used to obtain other compounds of this invention,such as 1,2,3,4,1,2,3',4-octamethyl ferrocene, l,3,l,3'-tetrahexylferrocene, and the like.

EXAMPLE II Bis-(metlzylcyclopentadienyl) iron Methylcyclopentadienyllithium is prepared according to the method of Organic Reactions, vol.VI, pp. 352 353, John Wiley and Sons, Inc., New York (1951). An othersolution of this material (1 mole) is slowly added with agitation to 0.5mole of anhydrous ferric chloride which is completely dissolved inanhydrous diethyl ether. The reaction is carried out in a vesselequipped with mechanical agitator and reflux condenser. The reaction isvigorous and exothermic. After addition of the lithium compound iscomplete, 500 parts of saturated aqueous ammonium chloride solution isadded to the reaction mixture with vigorous agitation. Three-hundredparts of benzene are then added to extract thebis-(methylcyclopentadienyl iron product. The ether-benzene layer isseparated from the aqueous layer and the ether and benzene removed undervacuum. The residue is distilled under vacuum to yieldbis-(methylcyclopentadienyl) iron in good yield. The product is isolatedas a dark orange to red liquid boiling at 240 C./760 ml.

d The above technique is applicable to other compounds of thisinvention, such as l,2,3,4,1,2,3',4'-octapropyl ferrocene,bis-(decylcyclopentadienyl) iron, and the like.

EXAMPLE III Monomerhyl ferrocene A 20 percent dispersion of sodium intoluene is preared by conventional methods. T this is added a mixture of70 percent of tetramethylcyclopentadiene and 30 percent ofcyclopentadiene. The total amounts of mixed cyclopentadienes amount to 1mole for every gram atom of sodium in dispersion form. This mixture isreacted for minutes at a temperature of 40 C. under a blanket of drynitrogen, and then 0.9 mole of ferric chloride, completely dissolved intetrahydrofuran, is added. After reacting for minutes at 40 C., thereaction mixture is worked up as described in the preceding examples,and a good yield of monomethyl ferrocene is obtained.

The procedure of Example 111 can be used with good results to obtainother mixed ferrocenes of this invention, both those in which there isone unsubstituted cyclopentadiene nucleus and those in which bothcyclopentadiene nuclei are substituted but with different alkyl groupsor with the same alkyl groups in different orientation on thecyclopentadiene ring. Thus, this method can be used for the preparationof 1,3-dinonyl ferrocene, 1,2,3,4,5- pentaethyl ferrocene,1,2,4,1',2,3'-hexaethyl ferrocene, l,2,3-trimethyl-l-isopropylferrocene, and the like. Generally an excess of the more highly:alkylated cyclopentadiene is used to overcome its slower reaction rate.A mixture of products is normally obtained, and this may be resolved byconventional means, usually vacuum fractionation.

EXAMPLE IV Decamethyl ferrocene A percent dispersion of sodium inmineral oil is prepared by conventional methods. To this is addedpentamethylcyclopentadiene in amount corresponding to 1 mole for everyWeight-atom of sodium present in the dispersion. To the sodiopentamethylcyclopentadiene thus prepared is added a solution of 0.5 moleof ferric chloride dissolved in tetrahydrofuran. Reaction is carried outunder anhydrous conditions for 15 minutes at C., and a good yield ofdecamethyl ferrocene is obtained.

EXAMPLE V e T etraoctyl ferrocene Tetraoctyl ferrocene is prepared in amanner identical with that of Example IV, except that1,3-dioctylcyclopentadiene is used as the starting material.

The new compounds of this invention find their greatest utility whenused as antiknock agents. To take advantage of this outstanding utility,we blend our new compounds with gasoline to obtain liquid petroleumhydrocarbon fuels containing alkyl cyclopentadienyl iron where thecyclopentadiene groups are substituted with l to 10 alkyl groupscontaining 1 to 10 carbon atoms, the total number of the carbon atoms inthe alkyl groups being 1 to 32, in amount sufficient to exert antiknockeffect. In so doing, We find that we achieve outstanding antiknockactivity and that the fuel blends are such that the antiknock agent isreadily blended, inducted, and distributed to the cylinders of theengine. We, in many instances, obtain best results when mixtures of ouriron compounds are blended with fuels according to the invention. Manyof the fuels so produced which contain mixtures of our alkyldicyclopentadienyl iron compounds possess superior inductibility anddistributability properties.

The fuel with which the antiknock agent of this invention can be blendedmay be any of the liquid hydrocarbon fuels of the gasoline boilingrange. These fuels are usually blends of two or more components and cancontain all types of hydrocarbons, including parafiins, both straightand branched chain, olefins, cycloaliphatics containing parafiin orolefin side chains, and aromatics containing aliphatic side chains. Thefuel type depends on base stock from which it is obtained and on themethod of refining. For example, it can be a straight run or processedhydrocarbon, including thermally cracked, catalytically cracked,reformed, hydroformed, etc. The boiling range of the components of thegasoline can vary from to about 430 F., although the boiling range ofthe fuel blend is often found to be between an initial boiling point offrom about 80 F. to 100 F. and a final boiling point of about 430 F.While the above is true for ordinary gasoline, the boiling range is alittle more restricted in the case of aviation gasoline. Specificationsfor the latter often require that the boiling range be from about 82 F.to about 338 F., with certain fractions of the fuel boiling away at aparticular intermediate temperature.

The hydrocarbon fuels in which the antiknock agent of this invention canbe employed often contain minor quantities of various impurities. Onesuch impurity is sulfur, which can be present either in a combined formas an organic or inorganic compound, or as the elemental sulfur. Theamounts of such sulfur can vary in various fuels from about 0.003percent to about 0.30 percent by weight. Fuels containing quantities ofsulfur both lesser and greater than the range of amounts referred toabove are also known. Our antiknock agents are less sensitive to fuelimpurities than are prior antiknock agents such as organolead compounds.

The amount of alkyl dicyclopentadienyl iron used to provide a finishedfuel of the desired octane number can be determined by one of theaccepted octane rating meth ods, such as the Research or Motor methodsof the American Society for Testing Materials (ASTM) or various roadrating methods. In general, however, we prefer to employ amounts notgreatly exceeding about grams of iron per gallon of fuel. For most fuelsfor use in automotive engines, the required amount will be substantiallybelow the maximum, while for fuels or aircraft engines where the octanenumber requirement is considerably higher, the amount of iron employedmay approach this maximum. Thus, the amount of iron in the form of alkyldicyclopentadienyl iron that can be added to a hydrocarbon fuel of thetype described above is from about 0.01 gram to about 10 grams pergallon of the fuel. When the fuel is employed in an ordinary automobileengine, an especially preferred range of concentrations of alkyldicyclopentadienyl iron in the fuel is from about 0.1 to about 4.0 gramsof the metal per gallon of fuel. Be cause of the high degree ofeffectiveness of our materials, these amounts give results comparable toor better than those obtained with substantially greater amounts of previous antiknocks. i

In addition to the alkyl dicyclopentadienyl iron antiknock agent andsulfur impurities, other components may also be present in thehydrocarbon fuel. Such other components may be antioxidants,stabilizers, dyes, and the like, specific examples of which areN,N-di-sec-butyl-pphenylene diamine, 2,4-dimethyl-6-tert-butylphenol,and the like.

Our antiknock agents can be employed with or without scavengers.Although we have found that satisfactory results are obtained withoutthe use of scavengers, they do aid in removing decomposition productsfrom the combustion chamber and thus are desirable. Among the scavengerswhich may be used are phosphorus and arsenic compounds, especiallyorganic phosphates such as trialkyl and triaryl phosphates (tributylphosphate, tricresyl phosphate, and the like), and also organiccompounds of boron, such as borate esters. When we use scavengers of theabove types, we find that they perform best in amount such that there isfrom 0.4 to about 1 atom of phosphorus, arsenic, or boron present foreach atom of iron in the fuel. Halogenated organic compounds may also beused as scavengers. The types and amounts specified in BartholomewPatent 2,398,281 are very satisfactory for this purpose.

The following illustrates typical fuels Within the scope of the presentinvention.

EXAMPLE VI To a motor fuel consisting of a blend of straight run,catalytically cracked, and polymer stocks, having an initial boilingpoint of 98 F. and an end point of 402 F., is added monomethyl ferrocenein amount so that there is 0.01 gram of iron present as monomethylferrocene per gallon of the fuel. This liquid hydrocarbon fuel possessessuperior antiknock qualities.

EXAMPLE VII To a motor fuel consisting of 100 percent catalyticallycracked gasoline having an initial boiling point of F. and an end pointof 425 F. is added l,2,l,2'-tetraoctyl ferrocene in amount correspondingto 0.1 gram per gallon of fuel. Also added to this mixture is triphenylphosphate in amount so that there is one phosphorus atom present forevery atom of iron in the fuel. This liquid hydrocarbon fuel possessesoutstanding antiknock qualities.

EXAMPLE VIII To an aviation gasoline of grade 100/ 130, comprisingisopentane, alkylate, aromatics, and straight run gasoline, and havingan initial boiling point of 82 F. and an end point of 330 F., is addedbis-(methylcyclopentadienyl) iron in amount so that 10 grams of iron arepresent per gallon of fuel. To this blend is also added tributyl boratein amount so that one atom of boron is present for every two atoms ofiron in the fuel. This liquid hydrocarbon fuel has high antiknock value.

EXAMPLE IX To a liquid hydrocarbon fuel consisting of a blend of lightcatalytically cracked naphtha, polymer stock, catalytic reformate, andlight straight run naphtha, containing butane and having an initialboiling point of 90 F. and an end point of 360 F., is added monoamylferrocene in amount corresponding to 4.0 grams of iron per gallon offuel. This liquid hydrocarbon fuel possesses outstanding antiknockactivity.

To illustrate the outstanding antiknock effectiveness of our newcompounds, we performed tests according to the Research method fordetermining antiknock activity (ASTM No. D908). This test, which isgenerally accepted as a method giving a good indication of fuel andantiknock behavior in commercial multi-cylinder engines, is conducted ina single-cylinder engine especially designed for the purpose andreferred to as the CFR engine. This engine has a variable compressionratio, and during the test the temperature of the jacket water ismaintained at 212 F. The engine is operated at a speed of 600 r.p.m.with a spark advance of 131 before top dead center. In such a test, werated bis-(methylcyclopentadienyl) iron in a fuel which consisted of 20volume percent diisobutylene, 20 volume percent toluene, 20 volumepercent isooctane, and 40 volume per cent n-heptane. The amount of ironcompound was chosen so as to give a concentration of 1.1 grams of ironas the bis-(methylcyclopentadienyl) compound per gallon of fuel. At thisconcentration, it was found that this amount of the iron compound raisedthe octane number of the fuel the same amount that required 1.7 ml. oftetraethyllead. Expressed in another manner, it was found that at thisconcentration one gram of iron as the above compound was equivalent inantiknock effectiveness to 1.6 grams of lead as tetraethyllead. It wasnot necessary to heat the induction system of the engine to induct theiron com-pound into the engine.

In a further test in which bis-(methylcyclopentadienyl) iron was used ata concentration of 3.3 grams of metal per gallon of fuel, the antiknockeffectiveness was such that one gram of iron as the above compound wasequivalent to 1 .7 grams of lead as tetraethyllead.

When the Research method antiknock rating is applied to other compoundsof this invention such as decamethyl ferrocene,1,2,3-triethyl-1,3-dipropyl ferrocene, monomethyl ferrocene,1,2,4-trioctyl ferrocene, 1,2,3,4,1,2,3, 4'-octamethyl ferrocene, andthe like, good antiknock effectiveness is likewise demonstrated.

When we tested bis-(cyclopentadienyl) iron under these circumstances, wefound that it had undesirable inductibility characteristics and that inorder to overcome these characteristics which resulted in stoppage ofthe carburetion system, it was necessary to preheat the induction systemto a temperature of 125 F. In contrast, when compoundsof this inventionwere used, no heating of the induction system was necessary. Ourcompounds were smoothly inducted into the engine with an unheatedinduction system.

A use to which the present compounds are particularly adapted is that ofa sup lementary antiknock. In other Word-s great benefits are obtainedwhen we blend our antiknocks and organolead antiknocks with gasoline toobtain a liquid hydrocarbon fuel containing an alkyl cyclopentadienyliron wherein the cyclopentadiene radicals are substituted with 1 toalkyl groups of 1 to 10 carbon atoms, in an amount suflicient toincrease the antiknock characteristics of said fuel, and containing anorganolead compound in an amount suflicient to increase the antiknockcharacteristics of said fuel.

When we utilize our compounds in such a manner, we obtain fuels whichgive a greater antiknock response than does the same fuel containing anequivalent amount of lead as an organolead compound, and at the sametime we achieve economical and technical advantages.

Among the organolead compounds we use in our leaded iron-containingfuels are tetraalkyllead compounds, such as tetramethyllead,tetraethyllead, tetraisopropyllead, dimethyldipro yllead,tetraoctyllead, and the like. We also use tetraaryl compounds, such astetraphenyllead, tetratolyllead, and so forth. We have unexpectedlyfound that when we use our iron compounds along with organoleadantiknocks in liquid hydrocarbon fuels, we obtain a greater antiknockeffect from the iron than we do when we use our iron compound in liquidhydrocarbon fuel in the absence of lead. We normally regulate the amountof organolead antiknock compound so as to be equivalent to 1.05 to 6.34grams of lead per gallon of fuel.

To illustrate this facet of our invention, we perform tests according tothe Research method (ASTM No. D 908) as described above. For example, weblended with the fuel described in the above tests 1 ml. oftetraethyllead per gallon of fuel and 1.1 grams of iron asbis-(methylcyclopentadienyl) iron per gallon. When this was testedaccording to the Research method, it was found that the iron compoundhad an antiknock activity such that each gram of iron was equivalent to2.7 grams of lead as tetraethyllead.

Thus, a valuable aspect of our invention consists of providing antiknockfluids which comprise organolead antiknock, a scavenger for theorganolead antiknock, and an alkyl dicyclopentadienyl iron wherein thecyclopentadiene radicals are substituted with 1 to 10 alkyl groups of 1to 10 carbon atoms, the total number of carbon atoms in said alkylgroups being 1 to 32. In such fluids the amount of the iron antiknockagent ranges between 20 to 80 percent of the combined amounts of ironand lead antiknock agents. The preferred type of scavenger for theorganolead antiknock agent is an organic halogen compound such asethylene dibromide, ethylene dichloride,

trichlorobenzene, dibromotoluene, dibromopentanes and butanes, andmixtures of the above and other halogenated organic compounds. Suchfluids may also contain a scavenger for the iron antiknock compound.Such scavengers may be of the type mentioned previously (phosphorus,arsenic, and boron compounds, etc). The amount of such scavengergenerally ranges from 0 to 1 atom per atom of iron in the fluid.

The following examples illustrate leaded fluids and fuels of thisinvention.

EXAMPLE X An antiknock fluid is prepared by blending parts by weight ofbis-(ethylcyclopentadienyl) iron with 20 parts by weight oftetraethyllead. To this mixture is added ethylene dibromide in amountequivalent to one theory based on the lead present. This mixture isfound to be an outstanding antiknock fluid.

When blended with the gasoline of Example VI such that the amount oftetraethyllead is equivalent to 1.05 grams of lead per gallon of fuel, aliquid hydrocarbon fuel having superior antiknock properties isobtained.

EXAMPLE XI We prepare an antiknock fluid which is composed of 20 partsby weight of bis-(isopropylcyclopentadienyl) iron, 80 parts oftetraisopro-pyllead, 1.0 theory of ethylene dichloride, and 0.5 theoryof ethylene dibromide based on the tetraisopropyllead employed, andsufficient tricresyl borate to give one atom of boron for every atom ofiron in the fluid. This fluid possesses superior antiknock properties.

When blended with the aviation gasoline of Example VIII in amount sothat the amount of lead present is 6.34 grams per gallon, a superiorantiknock liquid hydrocarbon fuel is obtained.

We claim:

1. An unsymmetrical di(lower alkyl substituted cyclopentadienyl) ironcompound wherein each lower alkyl cyclopentadienyl radical, by virtue ofdissimilar alkyl substitution, differs from the other lower alkylcyclopentadienyl radical.

2. A (lower alkyl-substituted dicyclopentadienyl) iron in which only onecyclopentadienyl group is substituted, said lower alkyl group being thesole substituent.

References Cited by the Examiner UNITED STATES PATENTS 2,398,281 4/1946Bartholomew 252-386 2,680,758 6/1954 Thomas 260-439 FOREIGN PATENTS1,080,357 5/ 1954 France.

OTHER REFERENCES TOBIAS E. LEVOW, Primary Examiner.

LEON D. ROSDOL, ARTHUR WINKELSTEIN, J. C. LANGSTON, T. L. IAPALUCCI, A.P. DEMERS,

Assistant Examiners.

1. AN UNSYMMETRICAL DI(LOWER ALKYL SUBSTITUTED CYCLOPENTADIENYL) IRONCOMPOUND WHEREIN EACH LOWER ALKYL CYCLOPENTADIENYL RADICAL, BY VIRTUE OFDISSIMILAR ALKYL SUBSTITUTION, DIFFERS FROM THE OTHER LOWER ALKYLCYCLOPENTADIENYL RADICAL.
 2. A (LOWER ALKYL-SUBSTITUTEDDICYCLOPENTADIENYL) IRON IN WHICH ONLY ONE CYCLOPENTADIENYL GROUP ISSUBSTITUTED, SAID LOWER ALKYL GROUP BEING THE SOLE SUBSTITUENT.